1. Field
This document relates to a touch screen apparatus and a driving method thereof.
2. Related Art
As home appliances or portable information devices are becoming more lightweight and slimmer, user input means is being switched from a button switch to a touch screen. A touch screen comprises a plurality of touch sensors.
U.S. Laid-Open Patent US 2010/0200310 (filed on Aug. 12, 2010) discloses a conventional touch screen (hereinafter, referred to as “Self capacitance touch screen”) comprising capacitive touch sensors at the crossings of X lines and Y lines crossing each other. The self capacitance touch screen scans the X lines and convert a signal received from the X lines into digital data by analog-to-digital conversion (hereinafter, referred to as “ADC”), and scans the Y lines and converts a signal received from the Y lines into digital data by ADC. The self capacitance touch screen determines that a touch sensor, positioned at the crossing point of an X line and a Y line and having a large change in capacitance before and after a touch, is a touch position. Such a self capacitance touch screen detects a touch position by analyzing digital data obtained by respectively sensing an X line and a Y line and converting them by ADC, and therefore may mistake a ghost point present at the same X and Y lines as an actual touch position. Accordingly, the self capacitance touch screen has the drawbacks that it has low multi-touch sensitivity and a complicated ghost detection and removal algorithm has to be additionally applied.
The self capacitance touch screen disclosed in U.S. Laid-Open Patent US 2010/0200310A1 senses X lines and Y lines in units of groups in a pre-scan step. Next, the self capacitance touch screen performs a re-scan step and a touch position detection step after an ADC step and a touch position detection step, thereby improving the accuracy of touch recognition. The self capacitance touch screen simultaneously scans X lies (or Y lines) in a group in the pre-scan step, which may lead to a reduction in touch sensing speed, as compared to the method of sequentially sensing all the X lines and Y lines each time a touch position is detected. However, the self capacitance touch screen has limitations in reducing touch sensing speed because it has to sequentially perform pre-scan, ADC, the execution of a touch recognition algorithm, re-scan, ADC, and the execution of the touch recognition algorithm.
A touch report rate is a rate at which coordinate data obtained by sensing all touch sensors present within a touch screen. The higher the touch report rate, the higher the continuity of touch input traces and the higher the touch sensitivity that a user feels. The touch report rate is in inverse proportion to total sensing time required to sense all of the touch sensors within the touch screen. That is, the longer the total sensing time, the lower the touch report rate. Accordingly, the self capacitance touch screen cannot achieve sufficiently high touch report rate.